In a new episode of the Medscape stroke update, University of Texas Southwestern Vice Chair of Neurology, Dr. Mark Alberts, discussed three related studies published in the November 17 online version of the New England Journal of Medicine, all which looked at warfarin dosing via a genetic testing model versus the traditional clinical algorithm in order to determine proper warfarin doses for patients.

Dr. Alberts noted that in all three warfarin dosing studies, enrolled patients presented with typical atrial fibrillation or similar thromboembolic risk, thus requiring a warfarin treatment.

In the video, Dr. Alberts explains that, “Typically, the primary endpoint was the time that it took to get the patients into a therapeutic range — an international normalized ratio (INR) of 2-3 — or the time that they stayed within a therapeutic range (again, an INR of 2-3). Secondary endpoints in all of these studies were clinically important outcomes such as ischemic or hemorrhagic events. In total, the 3 studies included slightly more than 2000 patients.”

Dr. Alberts goes on to note that in all three studies, analyzed either separately or combined, there was no substantial difference found in any of the patients’ clinical events, such as ischemic or hemorrhagic events, whose warfarin doses were set based on the results of genetic testing versus the routine clinical algorithm.

Moreover, “two of the three studies found no difference in the time span during which patients were within the therapeutic range with genetic dosing vs routine clinical dosing. Only 1 of the 3 studies found a statistically significant difference in terms of time within the therapeutic range using genetic testing vs a routine algorithm.”

While the conflation of results from the three studies appears authoritative, Dr. Alberts notes that the studies’ findings could be skewed by several flaws, such as differences in the patient population, sub-optimal pairing of the dosing algorithms, and many other possible other factors. There were also some subtle racial differences found in the studies, particularly among black patients, with genetic testing vs non genetic testing. However, this “was a subgroup-of-a-subgroup type of phenomenon,” according to Dr. Alberts who, given the fact that the pool of test subjects compiled in the three combined studies added up to more than 2000 patients, leads hims to the conclusion that, ” . . . there is no compelling evidence to routinely perform genetic testing when we are trying to calculate warfarin dosage.”